Refer to given Exercise and answer these questions.
a. For each study, on the basis of the information given, is it clearly a randomized experiment? If not, explain what additional information would make it clear that the study was a randomized experiment rather than an observational study.
b. For each study, discuss whether or not matched pairs were used. If it is not clear, explain what additional information would make it clear.
c. Discuss whether any of the studies would suffer from each of the following: the Hawthorne effect, interacting variables, ecological validity.
Exercise
Specify what an individual "unit" is in each of the following studies. Then specify what two variables were measured on each unit.
a. A study found that tomato plants raised in full sunlight produced more tomatoes than did tomato plants raised in partial shade.
b. A study found that gas mileage was higher for automobiles when the tires were inflated to their maximum possible pressure than when the tires were underinflated.
c. Ten randomly selected classrooms in a school district were assigned to have a morning fruit snack break, and another ten classrooms of the same grade level in similar schools were measured as a control group. The number of children who performed better than average on standardized tests was measured for each classroom.